Originally Posted by
iron eagel
CP I think with a bit of downhill you may be able to get the APC 6 X 6.5 to unload, I think the plane is clean enough. I would even try a 5.25X 6.25 stock apc as well it almost worked on a 58 oz plane. Figuring your plane weighing in just a little over a pound, and half the wing area of the stingray, it should be an interesting as far as speed on your plane. That prop would only load the motor enough to draw 635 watts at 26,700 rpm (.84 hp) so it might be an option to try.
As far as nitro I think I would try reducing the thickness of the head gasket first after reading about them wanting a 13:1 compression ratio for no nitro.
From what I read is they use thin oil and a syringe to measure the volume of the head at TDC and then calculate the compression after having measure the actual bore and stroke to determine the actual compression ratio so they have a real idea of what it is.
A couple caveats: these guys were really into fine tuning the engines, and they were not worried too much about the idle.
This engine ought to be run at 30,000 [I think].
I need to see what size prop "off the shelf" it can rev to 30,000....then use a HP / Thrust calculator to generate alternative sizes that take similar amount of HP to turn as my "control prop" used.
For example today..6.5 x 5.5 @26,500 requires 1.315 HP..so then I know I've got 1.3 HP to play with and the next move would be to see what it can do at 30,000 with 1.3 HP or slightly less.
So I plug in 5.5 x 6 @ 30,000 and find that it requires 1.067 HP. The resulting speed would be 170 mph and I would have a hard time believing that there is another 30+ MPH waiting to be had beyond what I witnessed today..but this is the approach I take with engines.
With electric motors that have perfectly flat torque curves you don't have this to consider. The engine has a peak "metabolism" almost like a living thing that has to operate at a certain pulse rate and blood pressure to be at it's best..
If I plug in 5.5 x 6.5 it requires 1.15 HP but now the over squareness is beyond what I've ever seen work in real life.
I have a feeling that the 5.25 x 6.25 needs to operate much faster than 30,000 and that if it's an E prop can it be drilled out to 5/16"..?